patch 9.0.0284: using static buffer for multiple completion functions

Problem:    Using static buffer for multiple completion functions.
Solution:   Use one buffer in expand_T.

src/version.c

@@ -707,6 +707,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    284,
 /**/
     283,
 /**/